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Acta Montanistica Slovaca Ronk16 (2011), slo2, 128-137

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Experimental

Materials

The circuit boards (PCBs) waste were selected as an input material for testing the leaching of gold, silverand accompanying metals. The chemical composition of the applied waste is given in Tab. 1.

Tab. 1. Chemical composition of the printed circuit boards (PCBs) waste under study.

Waste

Components[%]

Au Ag Cu Pb Zn Fe Sn Ni Al Pd

PCBs

(Slovakia) 0.014 0.08 47.5 1.4 1.1 10.36 3.3 0.85 2.7 0.003

Mechanical treatment and crushing of the PCBs wasteThe PCBs were mechanically pretreated by eliminating the semiconductors, condensers, and resistances.

Under industrial conditions, these parts are collected separately by specialised companies that use them forobtaining of heavy and noble metals. Residue of the PCBs are then crushed in special crushers. Subsequently theplastic parts are separated from the metallic ones. The metals are recycled and the plastic materials are dumped.

Hammer mill Omniplex 40/20 Ha (Alpine, Germany) crusher was used for treatment of the circuit boards(PCBs) waste. After crushing, the -800 m input material has been sieved and leached in a glass reactor usingleaching solutions for extraction of the observed metals as shown in the Tab. 1.

Leaching of Au, Ag and accompanying metals from the PCBs wasteFour types of leaching media have been applied:

PCBs waste was used to test the effect of sulphuric acid with hydrogen peroxide leaching of zinc, copper,

iron, aluminium and nickel.

Gold and silver recoveries from PCBs waste were tested through the medium of ammonium thiosulphate inthe presence of cupric sulphate and ammonia.

Lead and tin recoveries were tested through leaching by sodium chloride.

For palladium leaching aqua regia was used.

The leaching was investigated under conditions given in Tab. 2.

Tab. 2. Parameters for leaching of circuit boards (PCBs).

ParametersLeaching reagents

H2SO4+ H2O2 (NH4)2S2O3 + CuSO4.5H2O + NH3 NaCl HCl:HNO3(3 : 1)

Volume of glass reactor [ml] 500 500 500 500

Volume of leaching solution [ml] 450 450 450 450

Concentration of leaching reagents [M] 2 + 0.2 0.5 + 0.2 + 1 2 0.5

pH 6 9 6 2

Weight of sample [g] 45 40 34 33

Time of leaching [min] 480 2880 120 120

Stirring rates [s-1] 8.33 8.33 8.33 8.33

Temperature [C] 80 40 25 25

Results and discussion

Leaching of the crushed circuit boards (PCBs)The application of crushing proved to be an effective method of the PCBs waste pretreatment before the

extraction of gold, silver and accompanying metals into the leach liquors. For leaching Au, Ag andaccompanying metals from PCBs wastes the numbers of leaching media were used (Tab. 2). Their selection wasdone in a way that allowed selective leaching of the metals of interest. In order to make the chemical reactionsintensive, the presence of effective oxidation reagents was necessary. Their selection was done in a way thatallows selective leaching of the metals.

The dependence of zinc, copper, iron, aluminum, nickel, gold, silver, lead, tin and palladium recovery onthe leaching time for the PCBs waste is shown in Figs. 1-3.

Leaching of PCBs waste with sulphuric acid and hydrogen peroxide gave 76 % Zn, 85 % Cu, 82 % Fe,77 % Al and 70 % Ni recovery into the leachate after 480 min (Fig. 1).

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Jana Ficeriov, Peter Bal and Eberhard Gock: Leaching of gold, silver and accompanying metals from circuit boards (PCBs) waste

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0 60 120 180 240 300 360 420 480

0

20

40

60

80

100Me

[ % ]

Ni

Al

Fe

Cu

Zn

tL[ min ]

Fig. 1. Recovery of Zn, Cu, Fe, Al and Ni, Mevs. leaching time, tLfor circuit boards (PCBs) waste pretreated by Omniplex-hammer mill,

40/20 Ha (Alpine, Germany). Leaching reagent: H2SO4+ H2O2.

The leaching of as-received sample of the PCBs waste with the ammonium thiosulphate afforded only

16 % gold and 12 % silver into leach after 48 hours of leaching. The results for the same but the pretreated wasteby milling have accelerated the process of thiosulfate leaching. Pretreatment enables to achieve for the

ammonium thiosulphate leaching with ammonium 98 % gold and 93 % silver extraction after 48 hours ofleaching (Fig. 2).

Fig. 2. Recovery of Au and Ag, Mevs. leaching time, tLfor circuit boards (PCBs) waste pretreated by

Omniplex-hammer mill, 40/20 Ha (Alpine, Germany). Leaching reagent: (NH4)2S2O3 + CuSO4.5H2O + NH3.

However, when sodium chloride solution was applied, it was possible to achieve 88 % recovery of Pb and83 % recovery of Sn even after 120 min (Fig. 3). In the case of palladium 90 % recovery was achieved afterleaching in aqua regia solution after 120 min.

0 20 40 60 80 100 120

0

20

40

60

80

100Me

[ % ]

tL[ min ]

Sn

PbPd

Fig. 3. Recovery of Pb, Sn and Pd, Mevs. leaching time, tLfor circuit boards (PCBs) waste pretreated by Omniplex-hammer mill, 40/20 Ha

(Alpine, Germany). Leaching reagent: NaCl and HCl + HNO3 (aqua regia).

0 500 1000 1500 2000 2500 30000

20

40

60

80

100Me

[ % ]

tL[ min ]

AgAu

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Conclusion

For the achievement of a technologically acceptable recoveries, pretreatment was necessary. Comminutionby Omniplex-hammer mill 40/20 Ha (Alpine, Germany) was used for the purpose of our work. The pretreatmentwas necesssary in order to achieve a suitable input sample for leaching and it was positively reflected in the Au,Ag, Pd, Cu, Pb, Zn, Fe, Sn, Ni and Al leaching recoveries.

During the experiments it was possible to get excellent recoveries of all the metals that were of interest. Incase of Au, Ag and Pd the recoveries were 98 %, 93 % and 90 %. Thus the aim of the experiments was achieved.

The application of leaching reagents that facilitated appropriate kinetics and selective leaching of theinvestigated metals was found to be a very suitable method.

Hydrometallurgical approaches offer the opportunity to eliminate the loss of the metal yield from recyclingprocesses and have a potentially more significant environmental impact in implementation.

Acknowledgement: This contribution/publication is the

result of the project implementation "Research excellence

centre on earth sources, extraction and treatment"

supported by the Research & Development Operational

Programme funded by the ERDF.References

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